This invention relates generally to improvements in joint prostheses, particularly with respect to a ceramic-coated articulatory component such as a metal femoral ball in a hip prosthesis. The ceramic-coated articulatory component can be formed by vapor deposition of the like to have a relatively thin coating structure (about 5 microns) mirroring the surface finish or smoothness of the underlying metal substrate, and suitable for polishing to a smoother surface finish and a thinner coating structure (about 3-4 microns).
Joint prostheses such as hip prosthesis or knee prosthesis generally comprise a metal articulatory component fixed to patient bone and which moves against an associated bearing insert structure. In a typical hip or knee prosthesis, the articulatory component is formed from a biocompatible metal material such as cobalt chrome, titanium, or stainless steel to provide a strong and durable prosthetic base structure for engaging and moving against the associated bearing insert. In recent years, however, attempts have been made to construct the articulatory component from a ceramic or ceramic-based material to provide relatively smooth movement substantially in the absence of metal debris which can lead to prosthesis failure. One preferred ceramic-based material comprises silicon nitride, as disclosed in U.S. Pat. No. 6,881,229, which is incorporated by reference herein. Unfortunately, such ceramic materials have achieved relatively slow acceptance due to a fear of relatively low material toughness and associated fear of brittle fractures.
U.S. Pat. No. 6,881,229 discloses an improved ceramic material for use in joint prostheses, such as knee prostheses, wherein a ceramic-on-ceramic or a ceramic-on-metal articulatory interface is defined. The improved ceramic material comprises a doped silicon nitride (Si3N4) having relatively high hardness, tensile strength, elastic modulus, lubricity, and fracture toughness. Specifically, the improved doped silicon nitride ceramic has a flexural strength greater than about 700 Mega-Pascal (MPa) and a fracture toughness greater than about 7 Mega-Pascal root meter (MPam0.5). This high strength and high toughness doped silicon nitride ceramic achieves ultra-low wear over an extended service life, with dramatically reduced risk of brittle fracture.
In addition, U.S. Pat. No. 6,846,327 discloses improved ceramic materials for bone graft applications, wherein the ceramic material is designed to mimic structural characteristics of natural patient bone by including first and second regions of comparatively lower and higher porosity to respectively mimic natural cortical and cancellous bone structures. The preferred ceramic materials disclosed exhibit a flexural strength greater than about 500 Mega-Pascal (MPa) and a fracture toughness greater than about 5 Mega-Pascal root meter (MPam0.5). In use, the relatively low porosity region of the ceramic material provides high structural strength and integrity, whereas the higher porosity region is suitable for bone ingrowth to achieve secure and stable implant affixation.
The present invention comprises an improved joint prosthesis particularly wherein the articulatory component thereof is constructed from a metal substrate coated in the articulatory region with an improved high strength and high toughness ceramic material as disclosed, e.g., in U.S. Pat. No. 6,881,229 and/or U.S. Pat. No. 6,846,327, both references of which are incorporated by reference in their entireties.